The present invention relates to printer devices, and particularly although not exclusively to a method and apparatus for improving the detection of faulty or clogged nozzles in printer devices.
It is known to produce paper copies, also known as xe2x80x9chardxe2x80x9d copies, of files stored on a host device, e.g., a computer using a printer device. The print media onto which files may be printed includes paper and clear acetates for use in lectures, seminars and the like.
Referring to FIG. 1 herein, there is illustrated a conventional host device 100 in this case a personal computer, linked to a printer device 120 via a cable 110. Amongst the known methods for printing text and the like onto a print medium such as paper it is known to build up an image on the paper by spraying droplets of ink from a plurality of nozzles.
Referring to FIG. 2 herein, there is illustrated schematically part of a prior art printer device comprising an array of printer nozzles 220 arranged into parallel rows. The unit comprising the arrangement of printer nozzles is known herein as a printer head. In a conventional printer of the type described herein the printer head 210 is constrained to move in a direction 260 with respect to the print medium 200 e.g. a sheet of A4 paper. In addition, the print medium 200 is also constrained to move in a further direction 250. Preferably, direction 260 is orthogonal to direction 250. During a normal print operation, printer head 210 is moved into a first position with respect to the print medium 200 and a plurality of ink droplets are sprayed from a same plurality of printer nozzles 220 contained within printer head 210. This process is also known as a print operation. After the completion of a print operation the printer head 210 is moved in a direction 260 to a second position and another print operation is performed. In a like manner, the printer head is repeatedly moved in a direction 260 across the print medium 200 and a print operation performed after each such movement of the print head 210. When the printer head 210 reaches an edge of the print medium 200, the print medium is moved a short distance in a direction 250, parallel to a main length of the print medium 200, and another print operation is performed. The printer head 210 is then moved in a direction 260 back across the print medium 200 and another print operation is performed. In this manner, a complete printed page is produced.
In order to maintain the quality of the printed output of the printer device it is important that each instruction to the printer head to produce an ink drop from a nozzle of the plurality of nozzles does indeed produce such an fin drop. In conventional printers it is known to attempt to detect an ink drop as it leaves the nozzle during normal operation. In conventional printers this drop detection is used to indicate the end of life the printer head 210. Drop detection is known to be performed by a drop detection assembly 270. It is known to locate the drop detection assembly 270 outside of the region used for printing onto said print medium 200 and the drop detection assembly 270 is known to be located substantially close to an edge of said print medium 200.
Referring to FIG. 3 herein there is illustrated schematically a conventional drop detection system used in a production printer. An ink droplet 300 is sprayed from a nozzle 220 and the droplet subsequently follows the path 310. The path 310 traced by the ink droplet 300 is configured to pass between a light emitting diode (LED) 320 and a receiving photo diode 340. The light emitted by the light emitting diode 320 is collimated by a lens 330 to produce a narrow light beam which is detected by photo diode 340. In response to the light received, photo diode 340 produces a current which is amplified by amplifier 350. Conventionally, the supply of current and hence the brightness of the light emitted by LED 320 is configured so as to provide a constant current output from photo diode 340. For example, a decrease in the output current of photo diode 340 results in an increased current to LED 320. The resulting increase and brightness of LED 320 produces an increased output current of photo diode 340.
When an ink droplet 300, fired from nozzle 220, passes through the narrow light beam between LED 320, collimating lens 330 and photo diode 340 the ink droplet 300 partially blocks the light input into photo diode 340 as a result the output current of the photo diode decreases. The decrease in the output current of photo diode 340 is detected and, as described herein before, the input current into LED 320 is increased. However, due to the comparatively slow response time of the purgatory the increase in the input current into LED 320 produces an xe2x80x9cover shootxe2x80x9d in the output current of photo diode 340. Hence, the amplified current reduced by the photo diode 340 in the presence of a ink droplet 300 is to produce a characteristic pulse shape 350. In a conventional printer, the characteristic current pulse 350 produced by the passage of the ink droplet 300 is detected and counted by a prior art drop detection unit 370. In a conventional printer, a drop detection process comprises sending a signal to printer head 220 to fire an ink droplet 300 and attempting to detect the resulting characteristic current pulse 350 which is counted using drop detection device 370. The steps of firing a droplet and counting that the resulting characteristic current pulse is repeated six times. If four characteristic pulses 350 are counted from the six attempts to spray an ink droplet 300 then, in a conventional system, the printer nozzle 220 is considered to be functioning correctly.
However, because of the need for three separate optical components to produce the collimated light beam in conventional drop protection systems there is a greater possibility for misalignment between the various components. Any misalignment between the LED 320, collimating lens 330 and photo diode 340 results in the width of the region in which an ink droplet 300 may be detected being reduced. In addition, because prior art drop detection systems require that a plurality of droplets are sprayed and detected individually this results in a comparatively long detection time for a nozzle and waste of ink.
U.S. Pat. No. 5,430,306 (Hewlett Packard) discloses an opto electronic test device for detecting the presence of thermal-inkjet ink drops from a print head. The device includes an illumination-source, a collimating aperture, a lens for focusing a collimated light beam on to a detector which converts varying illumination intensities into a varying output electrical signal. The output signal of the detector is converted to a digital signal by an aialogue-to-digital converter (A/D) and the digitized output is stored as a series of samples in a memory device. Drop detection is effected by triggering an ink droplet to be sprayed from a pen nozzle, and after a delay of approximately 100 xcexcs, the droplet enters the collimated light beam. Occultation of the light input into the detector by the droplet causes a decrease in the output signal of the detector. The A/D converter samples the output signal of the detector and stores the sequence of digitized measurements in a memory. After a time delay, which is substantially longer than 100 xcexcs, a second ink drop is triggered to be ejected from the pen nozzle and after a delay the output of the detector is again digitized. These measurements are repeated for a sequence of, typically, 8 ink droplets and an average time-profile of the output of the detector is formed by a micro-processor. A drop signal is determined to be present if, for example, the peak-to-peak voltage of the average signal is greater than a threshold value.
In order to average out noise fluctuations and derive a usable drop signal it is necessary to repeat the steps of ejecting a droplet and measuring an output signal of a detector as the droplet reverses up the light beam a number of times.
Since there is a significant delay, much longer than 100 xcexcs, between each ink droplet ejected from the pen nozzle, the time required to test a printer head comprising a plurality of pen nozzles is significant.
The drop detector which is the subject of U.S. Pat. No. 5,430,306 is designed for use in a factory environment for testing the life of printer heads. The relative bulk of the strip light source, collimating apertures and focusing lens renders that invention unsuitable for implementation in individual production printer devices.
It is important, to improve the usability of production printers, to reduce the time required for characterizing a print head having a plurality of nozzles, as much as possible. However, the problem of characteristics becomes more difficult as the resolution of the printers becomes greater, as the droplet size reduces, because the signal to noise ratio of the drop detection signals reduces with reducing ink droplet size. In addition, it is important to develop more efficient use of printing ink.
The specific embodiments and methods according to the present invention aim to decrease the time required to test a printer device having a plurality of ink spray nozzles prior to printing, thereby increasing the number of tests performed on the nozzles yielding an improved knowledge of the functioning of the plurality of ink spray nozzles without affecting the printing rate of such devices and thereby improving printing quality and the functional lifetime of the plurality of ink spray nozzles.
Specific methods according to the present invention, recognize that by performing repeated measurements of an ink droplet near a drop detection device, the number of ink droplets that need to be sampled to provide an indication of a functioning printer nozzle may be reduced and hence the time taken to check the plurality of nozzles may be reduced.
According to a first aspect of the present invention there is provided an ink jet printer device characterized by comprising a printer head comprising a plurality of nozzles (400) for ejecting ink; means for detecting a sequence of droplets of ink ejected from said plurality of nozzles (540, 560) said detecting means operable to generate an output signal pulse in response to each ink droplet of said detected sequence of droplets of ink; and means for performing a measurement on each said output signal pulse of said detecting means (520), wherein for each said nozzle, said measurement means performs measurements on a number of output signal pulses corresponding to a number of detected ink droplets containing a predetermined volume of ink.
In the case of a nozzle ejecting black ink, the number of detected ink droplets per each said nozzle is preferably two. In the case of a nozzle ejecting ink of a color other than black, the number of detected ink droplets per each nozzle is preferably four. In each case, irrespective of the number of ink drops ejected, the nozzle is characterized on the basis of a predetermined volume of ink ejected from the nozzle. This predetermined volume can be ejected as one, two, four or another number of individual droplets.
Suitably, the means for performing measurements comprises a digital sampling means operable to produce a sequence of a plurality of digital sample signals, each quantized to represent an amplitude of a portion of said output signal pulse. The sampling means preferably performs a sequence of sampled measurements on a said output signal pulse at a sampling rate in the range 30 kHz to 50 kHz. A sampling period between samples in the range 12 s to 50 s has been found optimal, and in the best mode herein a sampling period of 40 s is applied. The detecting means is operable to output for each said detected ink droplet an analogue output signal pulse having an amplitude perturbation comprising a first portion of a lower amplitude than a steady state-amplitude output signal of 40 (s is applied. The detecting means is operable to output for each said detected ink droplet an analogue output signal pulse having- an amplitude perturbation comprising a first portion of a lower amplitude than a steady state amplitude output signal of 40 (s is applied. The detecting means is operable to output for each said detected ink droplet an analogue output signal pulse having an amplitude perturbation comprising a first portion of a lower amplitude than a steady state amplitude output signal of 40 (s is applied. The detecting means is operable to output for each said detected ink droplet an analogue output signal pulse having an among diode is an high intensity infra-red light emitting diode. The emitting element and receiving element are preferably located in the rigid locating means, which preferably comprising: a first housing (460); a second housing (450); and a rigid connecting member (470) being substantially straight and having a first end and a second end, wherein said first housing (460) is rigidly attached to said first end of said rigid connecting member and said second housing (450) is rigidly connected to said second end of said connecting member (470). Suitably the print head is aligned with the first and second housing elements such that ink droplets released from the print head follow a trajectory in which they pass between the emitter and detector mounted in the first and second housings respectively.
Preferably the first housing (460) has a first aperture (461); and said second housing (450) has a second aperture (451), wherein said first aperture (461) is located substantially opposite said second aperture (451), such that a beam of light may form a path between said first and second apertures.
In an optimal arrangement, said first housing means (460) houses said emitting element (540); and said second housing means (450) houses said receiving element (560), wherein said emitting element (540), said first aperture (461), said second aperture (451), and said receiving element (560) are configured to lie along a single substantially straight line.
Preferably the measuring means comprises: a processor; and a memory device (530), wherein said processor and said memory device are configured to operate for converting a said output signal into a plurality of integer number signals. The plurality of integer number signals are stored in the memory device. Preferably the measuring means is operable to measure said first output signal of said detecting means and convert said measured output signal into an integer number signal.
The invention includes an ink jet printer device configured to print onto a print medium, said printer device comprising: a printer head comprising a plurality of nozzles, said printer device characterized by further comprising; an elongate rigid connecting member having a first end and a second end; a first housing arranged for mounting an emitter device, said first housing rigidly attached to said first end of said elongate rigid connecting member; and a second housing arranged for mounting a detector device, said second housing attached rigidly to said second end of said elongate rigid connecting member, wherein said printer head is located with respect to said first housing and said second housing such that at least one ink droplet ejected from a nozzle of said plurality of nozzles of said printer head passes between said first housing and said second housing, in a trajectory which intersects a beam path between said emitter device and said detector device, said printer device further comprising means for measuring an output signal of said detector device, said measurement means operating to generate for a said nozzle a signal indicating a performance of said nozzle, in response to a said detector signal resulting from passage of said at least one ink droplet containing a predetermined volume of ink across said beam path.
According to a second aspect of the present invention there is provided a method for determining an operating characteristic of a nozzle of a print head of an ink jet printer device having an ink drop detection means, said nozzle being configured to eject a plurality of drops of ink said method characterized by comprising the steps of: sending an instruction to said print head to eject a predetermined sequence of at least one drop of ink from said nozzle said predetermined sequence of at least one drop containing a predetermined volume of ink; generating an output signal of said ink drop detecting means, said output signal generated in response to said pre-determined sequence of at least one ink drop; measuring said output signal of said ink drop detecting means; and determining said operating characteristic of said nozzle from said output signal.
Preferably said predetermined volume of ink lies in the range 30 picoliters to 100 picoliters.
As mentioned hereinabove, a said predetermined sequence, in the case of black ink suitably comprises two consecutively released ink drops, and for an ink color other than black, said predetermined sequence preferably comprises four consecutively released ink drops.
The step of measuring said output signal preferably comprises sampling said signal at a sample frequency in the range 30 kHz to 50 kHz. A sampling period between consecutive.samples is preferably in the range 12 s to 50 s, and optimally of the order 25 s.
Preferably the step of measuring said output signal of said ink droplet detection means comprises for each of said plurality of ink drops the steps of: waiting a fixed time period after said instruction is sent to said print head; performing a sequence of measurements on said output signal of said ink drop detecting means, wherein said sequence of measurements measure said output signal of said ink drop detection means at a plurality of time intervals.
Preferably said step of determining said operating characteristic comprises analyzing a sequence of at least one perturbation of said output signal produced in response to a predetermined volume of ink passing said detecting means.
Preferably the step of determining said operating characteristics of said nozzle comprises for each said ink drop, the steps of: identifying a largest value of output signal of said ink drop detecting means; identifying a smallest value of output signal of said ink drop detecting means; and subtracting said smallest value of output signal of said ink drop detecting means from said largest value of output signal level of said ink drop detecting means.
Preferably the step of determining an operating characteristic of a said nozzle comprises the steps of: determining a value of a perturbation of said output signal; and comparing said value of perturbation with a threshold value, wherein said threshold value is set at least six standard deviations above an average noise level of said output signal.
Preferably said total volume of said predetermined sequence of drop of ink passing said ink drop detecting means is configured to lie within a range of volumes which generates a said output signal having a peak to peak perturbation value of at least six standard deviations above a noise level of said output signal.
Suitably, the volume of said predetermined sequence of drops of ink lies substantially in a range 30 to 100 picolitres. The predetermined number of drops may be ejected from a said nozzle at a substantially constant ejection frequency.
According to a third aspect of the present invention there is provided a method for evaluating an operation of each nozzle of a print head comprising a plurality of nozzles, said nozzles being configured to eject a plurality of drops of ink, said method characterized by comprising the steps of:
a) sending an instruction to said print head to eject a pre-determined sequence of drops of ink from each said nozzle each said sequence of drops containing a predetermined volume of ink;
b) generating an output signal of an ink drop detecting means for each sequence of drops detected;
c) measuring said output signal of said ink drop detecting means for each sequence of drops detected;
d) determining an operating characteristic of a corresponding respective said nozzle from each said output signal.
Preferably said step of measuring said output signal of said ink droplet detecting means comprises the steps of: waiting a fixed time period after a said instruction is sent to said print head; and after said fixed time period has elapsed, performing a sequence of measurements on said output signal of said ink droplet detecting means to sample said output signal at a plurality of time intervals.
Preferably said step of determining an operating characteristic of said nozzle comprises for each signal corresponding to a said ink droplet ejected from said nozzle performing the steps of: identifying a largest value of output signal of said ink droplet detecting means; identifying a smallest value of output signal of said ink droplet detecting means; and subtracting said smallest value of output signal of said ink droplet detecting means from said largest value of output signal of said ink droplet detecting means, to obtain a peak to peak signal value representing a magnitude of perturbation resulting from a said ejected of ink droplet.
The method may comprise determining an operating characteristic of said print head from said plurality of nozzle operating characteristics.
According to a fourth aspect of the present invention there is provided a method of characterizing a print head of an inkjet printer comprising a plurality of nozzles capable of ejecting ink droplets, said method characterized by comprising the steps of:
selecting an individual nozzle of said plurality of nozzles;
generating a signal for instructing said nozzle to eject a predetermined sequence of at least one ink droplet;
continuously monitoring an analogue output signal of a detector device configured for detecting passage of said predetermined sequence of at least one droplet through a light beam;
digitizing said analogue output signal;
sampling said analogue output signal to produce a set of quantized digital samples of said output signal;
determining from said set of quantized samples a minimum level of said output signal;
determining from said quantized digitized samples a maximum level of said output signal;
determining a difference value between said maximum and said minimum levels;
comparing said difference value with a predetermined threshold level; and
depending on a result of said difference value determining whether said nozzle is satisfactory.
If said determined peak to peak value is greater than said threshold value, said nozzle may be accepted as satisfactory. If the determined peak to peak value is less than said threshold value, said nozzle may rejected as unsatisfactory.
The analogue signal comprises at least one perturbation, resulting from passage of a said ink droplet through said light beam, and preferably said step of sampling said output signal comprises sampling a said perturbation resulting from said ink droplet at a period between samples in the range 12 s to 50 s. Suitably, sampling said analogue output signal may be sampled at a sampling frequency in the range 30 kHz to 50 kHz.
Suitably the threshold level is set at least six standard deviations above an average measured noise level of said output signal.
The method may be repeated in steps i) to x) until a number of nozzles recorded as unsatisfactory exceeds a predetermined number.
The method may be repeated in steps i) to x) for each of said plurality of nozzles.
The method may further comprise the step of activating a printer head intervention procedure in which one or a plurality of unsatisfactory nozzles are automatically attempted to be cleaned if said number of unsatisfactory nozzles exceeds a predetermined quantity.
The method may further comprise the step of activating a process in which during a print operation, one or more satisfactory nozzles are used to eject a predetermined sequence of ink droplets in replacement of using said at least one unsatisfactory nozzle if said recorded number of unsatisfactory nozzles exceeds a predetermined quantity.
A said predetermined quantity of unsatisfactory nozzles is suitably set in the range 6% to 12% of a total number of nozzles comprising said print head.